On probing human fingertips in vivo using near-infrared light: model calculations

Abstract

Abstract. We probe volar-side fingertip capillary beds with nearinfrared laser light and collect Raman, Rayleigh, and Mie scattered light and fluorescence. The results are interpreted using radiation transfer theory in the single-scattering approximation. The surface topography of the skin is modeled using the Fresnel equations. The skin is treated as a three-layer material, with a mean-field treatment of tissue composition and related optical properties. The model, with a reasonable choice of tissue parameters, gives a remarkably accurate account of the features of actual measurements. It predicts the optimal values for the incident angle of the laser beam and the distance between beam and detector. It explains the correlated temporal changes in the intensities of elastically and inelastically scattered light caused by heart-driven pulses and why they are out of phase. With appropriate boundary conditions, the model can be used to discuss the scattering from ridged skin extruded conformally into an aperture in a metal surface under constant light pressure. The probing results suggest an inherent regularity and similarity in the anatomy and composition of surface and subsurface tissues of a wide range of skin types.

Noninvasive in vivo plasma volume and hematocrit in humans: observing long-term baseline behavior to establish homeostasis for intravascular volume and composition

“…They can also be a single set of values obtained by averaging the measured EE0 and IE0 values of a large number of people and this leads to Presently we are only concerned with relative changes and we have published 14,15,16 at least 3 different approaches to calibration i.e. finding the appropriate values of the parameters a-f including from numerical modeling and the in vitro measured absorption and scattering coefficients of plasma, RBCs and skin tissue.…”

“…We take the skin as being composed of three phases 16,17,18,19 , static tissue that deforms when mechanical stress is applied, and blood that itself is composed of 2 phases i.e. red blood cells and plasma that both move when mechanical stress is applied.…”

Dermal carotenoid measurements via pressure mediated reflection spectroscopy

“…An example is the NIR-Raman-based measurement of blood glucose concentrations in finger capillaries [31,32]. An example is the NIR-Raman-based measurement of blood glucose concentrations in finger capillaries [31,32].…”

Full Correction of Scattering Effects by Using the Radiative Transfer Theory for Improved Quantitative Analysis of Absorbing Species in Suspensions

“…Therefore, approaches based on separating absorption and scattering effects using fundamentals of light propagation are gaining more and more impetus in the field of spectroscopic quantitative analysis of highly scattering samples. [7][8][9][10][11][12] It should be noted however that these approaches also involve errors such as measurement errors and computational errors that have a direct impact on the prediction performance.…”